This invention relates to apparatus for continuous production of a slab made of polyurethane foam.
When slabs of polyurethane foam are made in accordance with the prior art, a huge mass of polyurethane foam, generally about 2000 mm(W).times.900 mm(H).times.2000 mm(L) is sliced into a plurality of slabs of a desired thickness of, for example, 100 mm. To be cured completely, such a mass must be allowed to stand for about 24 hours after the completion of foaming. During the curing process, the mass accumulates in it sufficient amount of heat of reaction to raise its temperature to about 150.degree. C. to 170.degree. C. This not only incurs the risk of fire but tends to cause yellowing of the polyurethane foam due to the internal heat build-up and thereby diminishes the commercial value of the product. In order to dissipate such a large amount of heat as efficiently as possible, a well-ventilated storehouse of fireproof structure having accommodation for huge porous masses as described above is required, which necessarily raises the cost of equipment.
Furthermore, if the final product has a sheet of, for example, fabric laminated on its surface, the manufacture requires a number of additional steps such as applying an adhesive to the surface of a slab and laminating a sheet onto the surface of the slab.
The invention described in U.S. Patent Application Ser. No. 838,449 aims chiefly to eliminate the abovementioned drawbacks of the prior art. More precisely, its primary object is to provide a method for continuous production of a slab of porous material, i.e. polyurethane foam, which comprises steps of providing a creamy foamable material of which the chemical reaction has been initiated, continuously feeding said foamable material to a horizontally moving trough to form a foaming mass on said moving trough, pressing the top surface of said foaming mass with a pressure means over a zone extending from a point just prior to the completion of foaming to at least the point of completion of foaming to make flat the top surface of said foaming mass, and horizontally moving said pressure means in synchronism with, and in the same direction as, said trough.
However, the inventors found that some of the slabs of polyurethane foam which had been produced by the method had cavities or cracks, which had been locally formed due to destruction of many of the cells constituting the foam. The method of Ser. No. 838,449 therefore cannot always provide slabs of a uniform density or porosity.